Block copolymers, which comprise hydrophilic and hydrophobic polymers covalently bound to one another, are, by definition, amphiphilic polymers. Above a certain concentration, called the critical micellar concentration (CMC) or critical aggregation concentration (CAC), the block copolymers can self-assemble to form supramolecular aggregates (micelles or nanoparticles) in aqueous medium. The micelles consist of two distinct regions—an interior region of hydrophobic polymer chains (the core region), which has the ability to solubilize hydrophobic molecules; and an outer region of well-solvated hydrophilic polymer chains (the shell region), which imparts colloidal stability. Block copolymers can be designed to exhibit low CAC (few milligrams per liter) and high thermodynamic stability, compared to low molecular weight surfactants. Generally, the size of block copolymer micelles is of the order of 10–40 nanometers (Reiss, G.; Hurtrez, G.; Bahadur, P. Block Copolymers. 1985, In Encyclopedia of Polymer Science and Engineering; Korschwitz, J. I. Ed.; Wiley-Interscience: N.Y.). Due to these properties, block copolymer micelles comprising hydrophilic-biocompatible and hydrophobic biodegradable segments have attracted considerable attention related to their use as nanosized carriers of poorly water-soluble drugs. These micelles can facilitate the solubilization of poorly water-soluble drugs, increase their circulation time in vivo and eventually target them passively or actively by means of targeting ligands to specific tissues (e.g. tumoral tissues) (Kataoka, K.; Harada, A.; Nagasaki, Y. 2001, Adv. Drug Deliv. Rev. 47, 113–131; Torchilin, V. P. 2001, J. Controlled Rel. 73, 137–172; Jones, M.-C.; Leroux, J.-C. 1999, Eur. J. Pharm. Biopharm. 48, 101–111.).